1. Field of the Invention
The present disclosure relates to the field of oil and gas exploration and production. More specifically, the present disclosure concerns a system and method for subterranean excavation for discharging particles and/or impactors from nozzles for excavating and angling the nozzles.
2. Description of Related Art
Boreholes for producing hydrocarbons within a subterranean formation are generally formed by a drilling system employing a rotating bit on the lower end of a drill string. The drill string is suspended from a derrick which includes a stationary crown block assembly connected to a traveling block via a steel cable that allows movement between the two blocks. The drill string can be rotated by a top drive or Kelly above the borehole entrance. Drilling fluid is typically pumped through the drill string that then exits the drill bit and travels back to the surface in the annulus between the drill string and wellbore inner circumference. The drilling fluid maintains downhole pressure in the wellbore to prevent hydrocarbons from migrating out of the formation cools and lubricates the bit and drill string, cleans the bit and bottom hole, and lifts the cuttings from the borehole. The drilling bits are usually one of a roller cone bit or a fixed drag bit.
Impactors have recently been developed for use in subterranean excavations. In FIG. 1 a schematic example of an impactor excavating system 10 is shown in a partial sectional view. Drilling fluid is provided by a fluid supply 12, a fluid supply line 14 connected to the fluid supply 12 conveys the drilling fluid to a pump 15 where the fluid is pressurized to provide a pressurized drilling circulating fluid. An impactor injection 16 introduces impactors into the fluid supply line 14; inside the fluid supply line 14, the impactors and circulation fluid mix to form a slurry 19. The slurry 19 flows in the fluid supply line 14 to a drilling rig 18 where it is directed to a drill string 20. A bit 22 on the lower end of the drill string 20 is used to form a borehole 24 through a formation 26. The slurry 19 with impactors 17 is discharged through nozzles 23 on the bit 22 and directed to the formation 26. The impactors 17 strike the formation with sufficient kinetic energy to fracture and structurally alter the subterranean formation 26. Fragments are separated from the formation 26 by the impactor 17 collisions. Material is also broken from the formation 26 by rotating the drill bit 22, under an axial load, against the borehole 24 bottom. The separated and removed formation mixes with the slurry 19 after it exits the nozzles 23; the slurry 19 and formation fragments flow up the borehole 20 in an annulus 28 formed between the drill string 24 and the borehole 20. Examples of impactor excavation systems are described in Ser. No. 10/897,196, filed Jul. 22, 2004 and Curlett et al., U.S. Pat. No. 6,386,300; both of which are assigned to the assignee of the present application and both of which are incorporated by reference herein in their entireties.
Shown in FIG. 2 is an example of a prior art drill bit 22 excavating in the borehole 24. The slurry 19 flows through the attached drill string 20 and exits the drill bit 22 to remove formation material from the borehole 24. The slurry 19 and fragmented formation material flow up the annulus 28. Nozzles (not shown) on the bit 22 bottom combined with the drill bit 22 rotation create an outer annular flow path with a concentric circle to form a rock ring 42 on the borehole 24 bottom. FIG. 3 provides an example of a bit 22 having side arms 214A, 214B, side nozzles 200A, 200B, and a center nozzle 202; each nozzle is orientated at an angle with respect to the bit 22 axis. As shown, the center nozzle 202 is angled about 20° away from the drill bit 22 axis, side nozzle 200A is angled about 10° away from the drill bit 22 axis, and side nozzle 200B is angled at about 14° from the drill bit axis. The side nozzles 200A, 200B are depicted on side arm 214A.
Illustrated in FIG. 4, side nozzle 200A is oriented to cut the inner portion of the exterior cavity 46. In this orientation the center nozzle 202 creates an interior cavity 44 wherein the side nozzles 200A, 200B form an exterior cavity 46. The side arms 214A, 214B fit into the exterior cavity 46 unencumbered from uncut portions of rock formation 270. By varying the center nozzle 202 orientation, the interior cavity 44 size can be varied. Similarly, the exterior cavity 46 can be varied by adjusting side nozzle 200A, 200B orientation. Manipulating cavity 44, 46 size can alter the rock ring 42 size thereby affecting the mechanical cutting force required to drill through the borehole 24 bottom. Alternatively, the side nozzles 200A, 200B may be oriented to decrease the amount of the inner wall 46 contacted by the solid material impactors 272. Shown in FIG. 5, a shallower rock ring 42 is formed by increasing the angle of the side nozzle 200A, 200B orientation.